This application claims the benefit of Korean Patent Application Nos. P2000-44443 and P2001-37132 filed Jul. 31, 2000 and Jun. 27, 2001, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly, to a liquid crystal display having reduced flicker and wide a viewing angle. The present invention also relates to a method of fabricating the above-mentioned liquid crystal display having reduced flicker.
2. Description of the Related Art
A ferroelectic liquid crystal (hereinafter, xe2x80x9cFLCxe2x80x9d) has a response time faster than other liquid crystal modes, as about several ten micro seconds to several mile seconds. This results from that the FLC has a spontaneous polarization characteristic without an electric field. The FLC also is able to realize a wide viewing angle without a special electrode structure and/or a compensating film, as such an In-plane Switching (IPS) mode. Accordingly, the FLC is spot-lighted because of being applied to a motion picture display representing a liquid crystal television.
The liquid crystal mode using such a FLC includes a deformed helix FLC (DHFLC), a surface stabillized FLC (SSFLC), an anti-FLC (AFLC), a V-shape FLC, a half V-shape FLC and so on. Since liquid crystal molecules in FLC mode among the above liquid crystal modes have only a bi-stable state, the SSFLC mode can be driven in a On/Off and has a disadvantage that it""s impossible to realize a gray scale. Meanwhile, the V-shape and half V-shape FLC modes allow the gray scale to be realized, because the liquid crystal molecules each has a mono stable state. In view of this point, the V-shape and half V-shape FLC have been actively studied. Furthermore, the half V-shape FLC has a primary alignment state better than that of the V-shape FLC. Therefore, the half V-shape FLC enhances a contrast ratio and enables the liquid crystal to be easily driven.
The half V-shape FLC uses a chiral smetic C (hereinafter, Sm C*) phase maintained at a normal temperature in a temperature induced phase transition process. Conventionally, in accordance with a temperature which becomes lower, the half V-shape FLC has a phase-transition in a sequence of a isotropic (hereinafter, xe2x80x9cIxe2x80x9d) phasexe2x86x92a chiral nematic (hereinafter, xe2x80x9cN*xe2x80x9d) phasexe2x86x92Sm C* phasexe2x86x92a crytal, as shown in FIG. 1. Referring to FIG. 1, if the temperature is low from a temperature maintaining the isotropic phase which does not have a director and a directional order, the liquid crystal molecules are aligned in the N* phase having the director. In sequence, when the temperature is lower than that of the N* phase, the liquid crystal molecules are aligned in the Sm C* phase having a constant director and a directional order, that is, a layer structure and a special tilt. When the phase of the liquid crystal is changed from the N* to the Sm C* through a smetic A phase, that is, at a second phase transition, a chevron or a bookself is formed to identify a layer normal direction with a rubbing direction, thereby allowing the liquid crystal molecules to be in the bi-stable state. In the bi-stable state, the liquid crystal molecules are stably positioned at both ends of a virtual cone. Meanwhile, in the liquid crystal having a phase transition sequence of the I phasexe2x86x92N* phasexe2x86x92Sm C* phase, a transition from the N* phase to the Sm C* phase as a first transition forces the liquid crystal layers to be inclined in two directions being symmetrized with a center at the rubbing direction, as shown in FIG. 2. At the phase transition from the N* phase to the Sm C* phase, if a direct current voltage is applied to the liquid crystal, only one of two layer directions is selected. Accordingly, the liquid crystal molecule in the Sm C* phase has the mono stable state forming an uniform alignment which a spontaneous polarization direction of the liquid crystal molecule identifies to a direction of electric field. The liquid crystal molecules of the mono stable state responds to an external electric field having a polarity contrary to that at the alignment and circles to draw an outer line of the virtual cone with a center in a normal line of a smetic layer, thereby controlling an amount of lights to be transmitted. As a result, the liquid crystal molecules in the mono stable state can realize the gray scale. A method of manufacturing the half V-shape FLC using such a phase transition process of the liquid crystal molecules will be described.
As shown in FIG. 3, a half V-shape liquid crystal cell includes liquid crystals injected between an upper substrate 1 and a lower substrate 11. The upper substrate is provided with a common electrode 3 and an upper alignment film 5 thereon, and the lower substrate 11 includes a thin film transistor array 9 and a lower alignment film 7. The thin film transistor array 9 and the lower alignment film 7 are disposed on the lower substrate 11. The liquid crystals are injected between the upper and lower substrates 1 and 11 at a temperature maintaining the N* phase or the isotropic phase, to be easy an injection of the liquid crystal. In sequence, if its temperature is low into a temperature allowing the liquid crystal to have the N* phase, the liquid crystal 15 are aligned in parallel with a rubbing direction of the alignment films 5 and 7, in a perpendicular direction. Then, an electric field is applied to the liquid crystal and the temperature is slowly low at the same time. To this end, the liquid crystal 15 changes into the Sm C* phase and become stable in the mono stable state having an uniform alignment which spontaneous polarization directions of the liquid crystal 15 are equal to a direction of the electric field, as shown in FIG. 3. Such a liquid crystal 15 being stable in the mono stable state responds to only an electric field having a polarity contrary to the electric field used at the alignment process. For example, if a negative polarity of electric field xe2x88x92E is applied to the liquid crystal 15 at the phase transition, the spontaneous polarization directions of the liquid crystal 15 are aligned to identify with a direction of the electric field xe2x88x92E. The liquid crystal 15 having such an alignment state are driven although the negative polarity of the electric field is applied to it. Accordingly, the liquid crystal 15 has a characteristic same as that of the primary alignment. Meanwhile, when a positive polarity of electric field +E is applied to the liquid crystals 15, the liquid crystal 15 is driven, that is, circles along with an outside of virtual cone structure by its spontaneous polarization. In other words, the alignment state of the liquid crystal 15 changes. Accordingly, it is possible to realize a continuous gray scale. As a result, the half V-shape mode of the liquid crystal 15 using a crossed polarizer have a characteristic of half V-shape voltage-transmission V-T as shown in FIG. 5.
Referring to FIG. 5, since the liquid crystal 15 of half V-shape mode, which a primary uniform alignment is formed by the negative polarity of electric field, are not driven, it is not almost the lights transmitted the liquid crystals 15. On and under the liquid crystal cell, there are disposed a first and a second polarizers having transmission axes orthogonal to each other. The first polarizer disposed under the liquid crystal cell has a transmission axis same as the primary alignment direction of the liquid crystal 15, and the second on the liquid crystal cell has another transmission axis orthogonal to the primary alignment direction of the liquid crystal 15. A linerly-polarization light passed the first polarizer is shielded by the second polarizer after transmitting the liquid crystal 15, thereby allowing a black state to be displayed.
On other hand, if the positive polarity of voltage is applied to the liquid crystal cell, the liquid crystal 15 of the half V-shape mode are driven to increase an amount of light transmitting the liquid crystal 15. Accordingly, the liquid crystal 15 of the half V-shape mode can realize the gray scale. This results from that the liquid crystals 15 driven by the positive polarity of voltage force a polarization direction of the linerly polarization light passed through the first polarizer to be changed in parallel with the transmission axis of the second polarizer such that the changed light is transmitted upwardly through the second polarizer.
As mentioned above, the liquid crystal 15 of the half V-shape FLC mode has a voltage-transmittance characteristic that the liquid crystal 15 respond to only any one of the positive and negative polarities. In order to prevent a deterioration of the liquid crystal, the half V-shape FLC is driven in a field inversion method as shown in FIG. 6. In this case, a brightness is charged during a driving voltage of one polarity, i.e., a driving voltage of positive polarity, is applied to the FLC, and not changed when a driving voltage of negative polarity is applied to the FLC, as shown in FIG. 7. Since the half V-shape FLC driven by the field inversion driving voltage enables a black state and a white state to be alternated, it is a disadvantage generating a flicker phenomenon. In order to prevent the flicker phenomenon, the half V-shape FLC must be driven in a high speed. In other words, a prior half V-shape FLC must be driven in a high speed of 120 Hz in order to display a 60 Hz of picture without the flicker phenomenon. However, the high-speed driving of the liquid crystal cell is limited and causes a rise in the cost of driving an IC by increasing the manufacturing cost of the LCD.
Accordingly, the present invention provides a liquid crystal display device and a method for fabricating a liquid crystal display device that substantially obviates one or more of the problems due to the limitations and disadvantages of the related art.
An object of the present invention is to provide a liquid crystal display device having reduced flicker and a wide viewing angle and preventing a flicker phenomenon in a half V-shape FLC.
Additional features and advantages of the invention will be set forth in the description that follows, and in part will be appeared from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof with the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a liquid crystal display device includes a first substrate; a second substrate; a first alignment layer on a first substrate; a common electrode on the second substrate, the common electrode is divided into at least two portions; a second alignment layer on the second substrate; and a ferroelectric liquid crystal layer between the first and second substrates, wherein molecules of the ferroelectric liquid crystal layer exist in at least two states having opposite alignment directions.
In another aspect, a liquid crystal display device includes a first substrate; a second substrate; an alignment layer on the first substrate; a common electrode on the second substrate; a second alignment layer on the second substrate; a ferroelectric liquid crystal layer having a photo-hardening material between the first and second substrates, wherein molecules of the ferroelectric liquid crystal layer exist in at least two states having different alignment directions.
In another aspect, a method for fabricating a liquid crystal display device includes the steps of forming a common electrode on a first substrate wherein the common electrode is divided into at least two portions; forming a first alignment layer on the first substrate having the common electrode; forming a second alignment layer on a second substrate; forming a ferroelectric liquid crystal layer between the first and second substrates to form a liquid crystal display panel; raising a temperature of the liquid crystal display panel; and applying a voltage to the at least two portions, the voltages having opposite polarities.
In another aspect, a method for fabricating a liquid crystal display device includes the steps of forming a first alignment layer on a first substrate; forming a common electrode on a second substrate, wherein the common electrode is divided into at least two portions; forming a second alignment layer on the second substrate; forming a ferroelectric liquid crystal layer having a photo-hardening material between the first and second substrates to form a liquid crystal display panel; raising a temperature of the liquid crystal display panel to a first level; applying a first voltage to the common electrode and lowering the temperature of the liquid crystal display panel to a second level; irradiating a first light onto a first area of the liquid crystal display panel to cure the photo-hardening material; raising a temperature of the liquid crystal display panel to a third level such that the ferroelectric liquid crystal layer in a second area of the liquid crystal display panel has a nematic (N*) phase; and irradiating a second light onto the second area of the liquid crystal display panel.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.